Vertical cities are high-density, mixed-use urban developments that maximize limited land through upward design, integrating residential, commercial, and recreational spaces. They offer benefits such as reduced urban sprawl, improved resource efficiency, and enhanced livability, but face challenges including high construction costs and social acceptance. Successful examples like Marina Bay Sands in Singapore showcase innovative infrastructure and sustainable design, while addressing potential drawbacks like social isolation and environmental impacts will be key to their future success.